Polymerization processes producing ethylene-alpha-olefin polymers generally comprise supplying a feed containing ethylene and at least one alpha-olefin and, optionally, a diene in a solvent to a reactor, and then carrying out polymerization in the presence of Ziegler-Natta catalysts or metallocene catalysts to form the polymer. The polymerization of ethylene and alpha-olefin is an exothermic process. Therefore, when the process is carried out in a solution process, for example using a liquid-full continuous flow stirred tank reactor, the heat of polymerization usually needs to be removed, for example, by using cooled solvent.
U.S. Pat. No. 7,119,157 discloses a method of preparing an EP(D)M elastomer, which includes precooling a reactive solvent to a temperature in the range of −80° C. to −100° C. Ethylene, at least one higher alpha-olefin having 3 to 18 carbons, and, optionally, at least one conjugated or non-conjugated diene having 5 to 15 carbons, are polymerized in the presence of the precooled reactive solvent. According to the method, the yield of the EP(D)M elastomer is increased by lowering the reaction temperature even though a conventional preparation device is used unchanged. Further, methods of controlling the yield of the EP(D)M elastomer and of recovering the EP(D)M elastomer are provided.
However, energy utilization and catalyst utilization in this type of process have not been considered extensively, especially in large-scale production plants. For example, where tons per hour of polymers are produced, pre-cooling the feed to −80° C. or lower may result in dramatic energy consumption, especially when increasing the feed rate of monomers, while decreasing the feed temperature in order to improve the yield of the polymer.
Therefore, there is a need for a process for preparing an ethylene-alpha-olefin polymer that provides improved energy utilization, catalyst utilization, and operability of the process, while providing constant attributes of the resulting polymer and without changing the existing polymerization plant.